OK, the nitty gritty for San Francisco is
If you come up interstate 5 north, and then take Interstate 580 west, you will come to the edge of the bay and the bay bridge. The bay bridge is actually part of Interstate 80. around half way across the bridge you cross that magic county line; you have just entered San Francisco county
a couple of hundred feet in the air.
When the Bay Bridge touches down on terra firma again you will be IN San Francisco Having approached it from the East side. From here you may catch the 101, or the 280, etc. to get to you final destination.
Having grown up in LA I must say that you are doomed to hit traffic somewhere. From
DisneyLand north you will cross several residential areas and business areas. As you approach one business area you will have traffic, as you pass it behind the traffic will go away
till you start to approach the next. Since I moved away about 6-7 years ago I can't say anything about current traffic patterns. Sorry.
Finally, having made the trip back and forth many many times on both the 101 and the 5, I stand by my 1 hour difference (exclusive of stops).
WEATHER: It tends to be cooler, and sometimes rain, but you never know. The 101 passes back and forth across the coastal mountains in a couple of spots. It will be noticeably sunnier and warmer when you're inland, but bring jackets.